1. Field of the Invention
The present invention relates to cellular radio systems and, more particularly, to the broadcast of relatively large short messages to selected groups of subscribers within such systems.
2. Description of the Related Art
Digital cellular radio communication systems have been introduced to virtually every part of the world and have experienced enormous growth over the last several years. Such systems are used not only for carrying voice traffic to and from the cellular radio subscribers of the system but also for data traffic such as electronic mail. Both voice and data traffic within a cellular radio system are conventionally point-to-point; that is, they are directed to or from a specific subscriber station operating within the network. However, the use of cellular radio systems for non-voice communication, i.e. data, is currently one of the fastest growing segments of this market.
Another communications function which has long existed in cellular radio systems is that of short message service (SMS). This is a feature in which a text message may be addressed to a specific subscriber within the cellular radio network and sent first to a message center. As soon as that subscriber is available to receive communications on the network, the SMS message is routed from the message center to the specific subscriber and is displayed as a text message on that subscriber""s terminal. Again, conventional SMS messages are also point-to-point in the sense that they are addressed to a specific subscriber within the network and routed to that subscriber in the same way as a voice call.
A new functionality which is desirable to incorporate into a cellular radio system is that of the simultaneous broadcast of short messages (BC-SMS) to a selected group comprising a plurality of subscribers. For example, it might be of interest to supply certain items of textual information simultaneously to a number of cellular subscribers who are members of a particular news group and operating within a particular region of the cellular network. Another example might be the use of BC-SMS facilities to broadcast a textual description of the proceedings of a football match to all the cellular subscribers currently in the immediate vicinity of the football stadium where the match is taking place.
The use of conventional SMS technology to implement BC-SMS functionality would be prohibitive in terms of cellular system resources. If a large BC-SMS message was sent into the network for simultaneous delivery to many different specifically addressed subscriber stations, the load could be prohibitive not only on the traffic channels of the system but also on the central processing unit (CPU) of the mobile switching center (MSC) controlling that portion of the cellular system. The larger in size the message is, the greater the load on the network will be.
One possible solution to the lack of system resources to implement BC-SMS messages via conventional point-to-point communication to a large number of cellular subscribers is the use of a shared channel of the system, such as a broadcast or paging channel, to broadcast the messages to all subscribers simultaneously. A drawback to a proposal to use a broadcast channel is that if a broadcast channel is allocated with sufficient capacity to handle maximum length BC-SMS messages, there will be a great deal of wasted bandwidth when no messages are sent. A drawback to a proposal to use the paging channel is that paging messages are all of a specifically defined structure and must be limited in length to avoid inhibiting the paging functionability. The BC-SMS messages contemplated in the present invention may be significantly longer than the paging messages normally sent on the paging channel and hence it would not be possible to send them by simply substituting a BC-SMS message for a paging message. Additionally, the paging channel is a critical element of the cellular system operation and uncontrolled displacement of its function by a significant number of long BC-SMS messages would result in decreased performance of the system in its ability to locate mobiles for conventional voice calls to the mobiles.
The method and system of the present invention provides a solution to these problems and enables BC-SMS messages to be implemented in an orderly and a efficient manner within a cellular radio communication system.
In one aspect, the present invention includes broadcasting short messages to selected groups of mobile subscribers within a cellular radio system. The message to be broadcast is organized into a broadcast protocol having a recipient group address, message identification indicia and message contents and then broadcast on a shared broadcast resource of the cellular system. The organized broadcast message is recognized at the selected groups of subscriber stations within a selected portion of the cellular system. The paging channel of selected radio base stations within the cellular system in the geographic area within which members of the selected groups of mobile stations are believed to be present is used to broadcast the message.
In another aspect, the present invention includes a protocol structure for a paging message (PBC) to be broadcast on the paging channel of a radio base station of a cellular radio system. The PBC messages carry a relatively large short broadcast message (BC-SMS) to be broadcast to a selected group of mobile subscriber stations operating within the system after separating the BC-SMS message into a plurality of smaller segments. The structure of the protocol includes the essential elements of a conventional paging message which are necessary in order to identify the PBC message as such to a particular category of mobile subscriber stations within the system, a broadcast group address identifying the mobile subscribers for which the BC-SMS message is intended, a message ID number identifying the BC-SMS message within the system, a message segment number for each of the separate segments into which the BC-SMS message is separated for identifying each particular segment of the message to be broadcast on each paging message, and the message contents of the message segment to be broadcast. The conventional paging message is modified to be unrecognizable to a first group of mobiles but recognizable to a second group which includes the particular category of mobile stations for which the PBC message is intended.
In yet another aspect, the present invention includes broadcasting short messages to selected groups of mobile subscribers within a cellular radio system by composing at a message source a short message to be broadcast (BC-SMS). The BC-SMS message has a broadcast group address comprising a geographical part identifying the geographical region of the cellular system to which the message is directed and a function group part identifying the particular selected groups of mobile subscriber stations to which the BC-SMS is to be delivered. The BC-SMS message information is forwarded from the message originator to a message center within the cellular system where it is organized into a message in accordance with the invention and then sent from the message center to the mobile switching center (MSC) of the system associated with the geographic part of the BC-SMS message broadcast group address. The organization of the message within the message center includes determining whether the size of the BC-SMS message to be broadcast is greater than a predetermined number of octets. If so, the BC-SMS message to be broadcast is separated into a plurality of separate segments, each segment to be separately broadcast as a paging message on a radio base station of the system. A sequence of paging messages (PBC) is formatted with each having the following parts: a broadcast group address identifying the mobile subscribers for which the message is intended; a message ID number identifying the message within the system; a message segment number for each of the separate segments into which the message is separated and identifying each particular segment of the message to be broadcast on each paging message; and the message contents of the message segment to be broadcast. The PBC messages carrying said BC-SMS message are sent from the message center to the MSC associated with the geographic part of the address. The MSC then sends the PBC message to all of the base stations in the area associated with the address and they are sequentially broadcast from all radio base stations within the area of the cellular system along with ordinary PBC messages in accordance with a priority determined to ensure that the paging functionality of said system is not seriously adversely affected.